In the next year we plan to continue our investigations on the expression of the mitochondrial genome in animal cells. In particular, the physical, chemical, and metabolic properties of the discrete poly (A)-containing RNA coded for by mitochondrial DNA and the amino acid specifically of the tRNA coded for by mitochondrial DNA will be investigated. The gene mapping of the HeLa mitochondrial genome by electron microscopic-biochemical means will be extended to the poly (A)- containing RNA components and to the specific tRNA genes. The metabolic properties and the functional significance of the discrete products of mitochondrial protein synthesis in HeLa cells will be analyzed.